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Network Review Edge Device – Connects hosts – Sees little traffic (GB) – Sees a small number of flows Implications: – Can do per flow processing. – Can store per for state Core – Connects other switches – Lots of traffic (TB) – VERY Expensive – See a lot of flows Implications – Can’t do per flow processing! – Can’t store per flow state

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Router Review Fast path/data path – Specialized H/W Very Expensive Takes 3-5 years to change – Performs processing on every packet Very very fast Slow Path/control plane – Has general purpose CPU – Runs routing algorithms – Only works on a few packets Very very slow – Can’t process all packets

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Indirect Control leads to … – 62% of network downtime in multi-vendor networks comes from human-error – – 80% of IT budgets is spent on maintenance and operations.

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13 An Architecture Question to Study How should the functionality that controls a network be divided up? Important: everyone hates net outages Practical: solutions can be implemented without changing IP or end-hosts Relevant: trends toward separating decision- making from forwarding Unsolved: problem is not solved by running BGP/OSPF on faster servers

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14 Our Proposal: Dissemination and Decision Planes What functions require a view of entire network and network objectives? Path selection and traffic engineering Reachability control and VPNs ! Decision plane What functions must be on every router to support creation of a network-wide view? Topology discovery Report measurements, status, resources Install state (e.g., FIBs, ACLs) into data-plane ! Dissemination plane